One possible bug, the page numbers seem to jump with epub format. I am assuming that this is because actual page numbers are in the format, as in one case I can see the page flows, it is just the number that jumps (from 3 to 5).

This is probably a "feature", rather than a bug. The page number in FBReader is based on a fixed number of bytes per page, not on how much text is currently displayed per screen. So it is possible for the page number to jump by 2 (or not change at all) after a page turn.

The advantage of this is that the page number is independent of the font size (and the device). The disadvantage is that it isn't very similar to how we expect page numbers to behave.